1. Field of the Invention
The present invention relates to a semiconductive glaze product which is applied to the surface of a ceramic insulator to thereby form a conductive glaze insulator, to a method for producing the glaze product, and to an insulator coated with the glaze product.
2. Background Art
Conventionally, a ceramic insulator has been coated with a glaze so as to enhance the strength of the insulator. This makes use of the “compression effect” of glaze, in which the glaze layer compresses the insulator by means of the difference in thermal expansion coefficient between the insulator and the glaze (in general, the thermal expansion coefficient of an insulator is higher than that of a glaze). Among various glazes, a semiconductive glaze is applied to the surface of an insulator for allowing a small amount of current to flow through the surface of the coated insulator, to thereby remove dirt or contaminants adhering thereto and improve the insulator's electrical insulating characteristics, which may otherwise deteriorate when dirt or contaminants deposit on the surface of the insulator.
The applicant company of the present invention has disclosed such semiconductive glazes; specifically, a fritted tin oxide-antimony oxide-based conductive glaze (see Japanese Patent Publication (kokoku) No. 49-3816, page 6); a tin oxide-antimony oxide-niobium oxide-based conductive glaze (see Japanese Patent Publication (kokoku) No. 55-37804, page 1); and a tin oxide-antimony oxide-based conductive glaze in which ρ distribution is regulated (see Japanese Patent Publication (kokoku) No. 59-23051, page 1).
The aforementioned conductive glazes have a high thermal expansion coefficient of about 0.32%. When such a conventional conductive glaze is applied to a base material having a high thermal expansion coefficient (e.g., a cristobalite base material having a thermal expansion coefficient of about 0.42%), the difference in thermal expansion coefficient between the conductive glaze and the base material is about 0.10 percentage points, and thus the glaze exhibits sufficient compression effect.
However, when the aforementioned conventional conductive glaze is applied to a non-cristobalite base material having a thermal expansion coefficient of about 0.38%—which base material, in recent years, has been employed in, for example, an LP insulator, an SP insulator, or a porcelain bushing—since the difference in thermal expansion coefficient between the glaze and the base material becomes as small as 0.06 percentage points, the compression effect of the glaze is lowered by such a small difference in thermal expansion coefficient, leading to a problem that the strength of the resultant insulator is lowered; i.e., the insulator fails to attain a predetermined strength.